The invention relates to a brake booster, in particular, to the construction of coupling thereof with a master cylinder.
A brake booster includes a diaphragm disposed within an enclosed shell to divide the interior thereof into a plurality of pressure chambers to produce a pressure differential therebetween which is effective to move a power piston back and forth, thereby producing a booster action. To meet the requirement for a reduced weight of a vehicle, the weight of the brake booster is also reduced, by reducing the sheet thickness of the shell. However, the reduced wall thickness of the shell presents a problem in respect of a degraded strength. As is well known, a master cylinder is secured to the brake booster at the front side of the shell by means of mounting bolts. Tension of an increased magnitude is applied to the mounting bolts during operation of the booster, presenting a problem in respect of the strength of the mounting area.
To solve the problem, a variety of boosters have been proposed which attempt to increase the strength of the mounting bolt area by the provision of a strengthening plate, as disclosed in (1) Japanese Utility Model Publication No. 17,402/1985, (2) Japanese Laid-Open Patent Application No. 99,450/1982 and (3) Japanese Laid-Open Utility Model Applicaton No. 63,769/1982.
In the first proposal the strengthening plate is not welded to the shell, and hence cannot exhibit a satisfactory strengthening function. In the second proposal, projection rings at two locations have an equal diameter and are welded simultaneously, resulting in a failure to assure a uniform welding quality. In addition, the reduced diameter of the rings fails to provide a sufficient strengthening effect. In the third proposal, a spot welding is employed, which is subject to a stress concentration in the region of the spot welding. All of the described proposals have defects in one or other respects.